Catheters are widely used in medical procedures, providing access to internal bodily passages and cavities for both diagnostic and therapeutic purposes without surgery. Catheter use has enabled physicians to perform sophisticated non-surgical procedures in such diverse regions of the body such as the heart and coronary arteries, the brain, and the genito-urinary tract. Catheters offer significant benefits in these procedures by lowering the cost of the procedure and reducing risks.
A critical step in catheter procedures is the insertion of the catheter into the body and the placement of the catheter tip at the appropriate location. Precise placement of the catheter tip is often critical to the function to be performed by the catheter, since the function must often be performed at a highly localized region of internal tissue without affecting adjacent areas. Placement is particularly difficult when the bodily passage is very small in diameter as well as long and tortuous, and when the interior wall of the passage is delicate and susceptible to puncture.
There are numerous examples where catheter tip placement can be critical to the success of the procedure. The removal of plaque from arteries in cardiovascular surgery is one example. Accurate steering is important in this procedure in reaching or sub-selection of the affected arteries and the location of the plaque or thrombi. In obstetrics and gynecology, directional control is important when catheters are used for the selective removal of excessive tissue and cyst growth in dilatation and curettage procedures. The same is true for the use of catheters used to deliver site-specific treatments for ovarian cancer. Directional control is also important in catheter-based urology procedures, such as the selective removal of malignant prostate tissue and the treatment of urinary tract blockages and infections. Improved biopsy methods use catheters to reduce the incidence of trauma in healthy tissue. Directional control is particularly important in neurosurgery involving the use of catheters to remove intracranial hematomas and similar procedures. Due to the high degree of tortuosity of the vasculature, sub-selection of the affected artery is difficult, requiring a long time and a high degree of dexterity by the clinician. Other procedures and applications where steering capability is important will be readily apparent to the experienced medical practitioner.
Steering mechanisms have been devised for directing the distal tip of the catheter in a desired direction by remote control from the proximal end. One such mechanism includes a series of wires running the length of the catheter body on either side of its central axis and terminating in shims or thin strips at the distal end of the catheter. The operator steers the catheter by applying tension to one shim relative to the other, thereby causing the distal end to curve in the direction of the wire to which tension has been applied. This mechanism has disadvantages, however. The wires and the mechanism at the proximal end for selectively applying tension are unwieldy and susceptible to breakage. Furthermore, the wires offer limited directional choice without twisting the entire catheter to achieve angular adjustments relative to the catheter axis.
Guidewires are widely used to assist in the placement of catheters in locations which are difficult to reach. A guidewire is typically of very narrow diameter to fit within the lumen of a catheter. This permits the operator to slide the catheter over the guidewire once the guidewire has been properly positioned. It also permits the operator to remove one catheter and replace it with another without removing the guidewire, thereby avoiding the cumbersome procedure of independently relocating the catheter tip to the region of interest. The steering of a guidewire is generally accomplished by incorporating a slight curve into the guidewire construction at its distal tip, the tip being resilient in construction to resume the curvature when relaxed. This enables the operator to direct the guidewire tip laterally into branches of the vessel. To do this, however, the operator must rotate the guidewire from the proximal end so that the curve points in the desired direction.
A further steering method described in the literature involves the use of laterally directed jets of fluid at the distal tip of the catheter, where the reaction force from the jets causes the tip to bend. A disclosure of jets of this type is found in Boretos, U.S. Pat. No. 4,403,985, issued Sep. 13, 1983. The reaction force principle is also used to advance a catheter into the bodily passage by directing the jets at an acute angle relative to the catheter axis. By simultaneously actuating two or more jets positioned at intervals around the circumference of the catheter tip, the net reaction force will be directed along the catheter axis in the distal direction. Disclosures of catheters utilizing this effect are found in Papantonakos, U.S. Pat. Nos. 4,717,381, issued Jan. 5, 1988, and U.S. Pat. No. 4,769,006, issued Sep. 6, 1988, and Schubert, U.S. Pat. No. 4,475,902, issued Oct. 9, 1984. One difficulty with these systems is that they require several independent lumens extending the length of the catheter and independent ports at the catheter's distal tip, limiting the space available at the tip for functional (therapeutic or diagnostic) elements.
These and other disadvantages of the prior art are addressed by the present invention.